Dairy Barn Methane Levels and Feasibility of Thermal Catalytic Oxidation for Net Climate Benefit

Thermal catalytic oxidation has emerged as a promising technique to destroy methane from dilute sources, such as agricultural emissions in engineered indoor environments. The concentration of methane and total volumetric treatment requirements must be understood to evaluate the feasibility of this approach, particularly with respect to economic and environmental viability. Here, dairy farm field sampling campaigns were conducted in New England dairies (free stalls with 600-1, 200 head of cattle in both convection and tunnel ventilation) to establish a robust framework to evaluate the climate-benefits and cost-effectiveness associated with deployment of thermal catalytic methane oxidizers in these housing styles. Methane (CH4) levels ranged from 2-70 ppm in summer and 2-102 ppm in winter due to reduced ventilation during cold weather. Temperatures ranged from 24. 2 to 33. 3 and 3. 0-15. 5 °C, relative humidity (RH) ranged from 28. 3 to 56. 5 and 26. 5-85. 4% RH, and ammonia ranged from 0. 0 to 6. 5 and 0. 0-8. 0 ppm in summer and winter, respectively. Presuming a thermal catalytic reactor temperature of 400 °C and recovery of 90% of the heat generated from the methane destruction, climate beneficial operation requires a CH4 concentration of at least 10 ppm (wind), 33 ppm (solar), 245 ppm (grid), and 140 ppm (natural gas) for a 100-year GWP. At a reactor temperature of 400 °C and 100 ppm of CH4, the energy cost alone per tonne of CO2e removal would be 591, 425, and 173 for solar, wind, and biogas energy, respectively, and over 10, 000 for both grid and natural gas. The use of onsite biogas provided a net climate benefit at all methane concentrations and operating temperatures due to the destruction credit from manure-derived fuel. However, the large dairy barn air flow rates (250 cfm cow-1 in winter and 2, 000 cfm cow-1 in summer) translate to high power requirements (9-74 MW), challenging the practical implementation of renewable energy sources. This highlights the steep challenge associated with postrelease enteric methane destruction.